A supermarket will this week start selling "hope" alongside its baked beans and bananas, in the latest initiative aimed at persuading the cash-strapped public to give more money to charity.

Wooden blocks roughly the size of box of Maltesers branded with the single word "hope" will be interspersed with groceries at branches of Budgens in Crouch End and Belsize Park in London in a pilot scheme. Shoppers will be urged to take them to the till where they will be charged £1 per block which the retailer will forward to the Alzheimer's Society – the block is returned to the shelf.

The tactic is aimed at countering a national slump in charity donations. During the economic downturn from 2007, voluntary income received by the 1,000 biggest charities has fallen more than a fifth from £11.2bn to £8.7bn according to the Charities Aid Foundation.

"We are putting charitable giving in the context of people's everyday routines and it makes it more accessible," said Simon Horton, part of the creative team at the advertising agency JWT which devised the "hope" idea. "Everyone goes shopping and while you are in the mindset of spending money it is easy to put £1 on your bill. You are not being bombarded by anybody on the street and it is on your terms. We are making hope a commodity. You are buying a bit of hope in the same way as you are buying your beans."

Horton said that if the idea takes off, the blocks could be branded for different charities and distributed appropriately in store, for example those in aid of children's charities could be stacked next to nappies and baby food.

"Customers are very focused when they come into the supermarket," said Andrew Thornton, owner of the Budgens branches where the scheme will be tested. "So it makes sense that this method of donating is very quick." He said they will try placing the blocks in different locations, starting with beside the impulse-buy chocolate bars at the till queue. Budgens will cover the administration cost of the scheme and the advertising agency will pay for the blocks.

The idea comes amid growing interest among fundraisers in how to piggyback on the public's existing spending habits. Government ministers are reported to be encouraging a scheme that would allow supermarket shoppers to round up their bills to the nearest pound while Link, the cash machine network, has announced it is planning to programme its ATMs to ask users if they want to donate to selected charitable causes when they withdraw cash.

"More fundraisers are chasing less money and since the government's statutory funding cuts were announced we have seen organisations in education, the arts and health enter the fundraising arena," said Simon Morrison, director of marketing at the Institute of Fundraising. "It means established charities are having to be ever more innovative."

He said the idea had the potential to allow charities to reach groups that traditionally give least – the young and the poor – who do not respond as well to traditional fundraising methods such as direct mail, advertising and social events.

"We're always looking for innovative and quirky new ways to raise money and the 'blocks of hope' initiative does just that," said Jennifer Moseley, community fundraising manager for the Alzheimer's Society.